LibJS: Move has_constructor() from NativeFunction to FunctionObject

At a later point this will indicate whether some FunctionObject "has a
[[Construct]] internal method" (separate from the current FunctionObject
call() / construct()), to help with a more spec-compliant implementation
of [[Call]] and [[Construct]].
This means that it is no longer relevant to just NativeFunction.

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h

@@ -71,6 +71,8 @@ public:
     // This is for IsSimpleParameterList (static semantics)
     bool has_simple_parameter_list() const { return m_has_simple_parameter_list; }
 
+    virtual bool has_constructor() const override { return true; }
+
 protected:
     virtual bool is_strict_mode() const final { return m_strict; }